In general, a disc drive contains one or more discs capable of magnetically storing information. The information is read and written to specific locations on the disc or discs using magnetic transducers, commonly known as heads, that "fly" above the disc surface. Head positioning apparatus is provided in the form of an actuator arm assembly.
The actuator arm assembly consists of a substantially triangularly shaped actuator arm. Traditionally the arm is constructed from a low mass material such as cast aluminum. The arm is designed to pivot about a centrally located pivot bore. The bore cooperates with a bearing system surrounding a fixed shaft enabling the arm to pivot smoothly about the shaft.
At one end of the arm is attached a means for moving the arm about the shaft. Typically, the motion is accomplished by a moving coil magnetic motor having the motor coil attached to the arm. Activating the motor coil causes the actuator arm to pivot about the shaft.
Attached at the other end of the arm are transducers for receiving and depositing information from/to the discs. The transducers are commonly known as read/write heads. The electrical signals received by the heads are transmitted via flexible cabling to a signal processing circuitry located elsewhere in the disc drive.
To ensure accurate alignment of the heads over desired positions on the discs, the arm must be physically stable during all suspected disc drive operating conditions. The main concern is that the bearing system be stable and have minimum friction over a large operating temperature range. To reduce arm tilt relative to the longitudinal axis of the shaft at a nominal temperature, the bearings are preloaded. However, preloading increases the friction in the bearing system. Additionally, as the temperature varies about the nominal value the bearing system and shaft expands and contracts relative to the aluminum arm causing fluctuations in the bearing preload force which results in fluctuations in the actuator arm tilt. To limit the tilt over all temperature ranges, the bearing preload is increased which also increases the friction.
In small disc drives, there is not enough space along the shaft to allow a spring to be used to supply the preload. Instead, a dead weight technique is used. This technique uses the spring weight of the bearing structure itself to provide the preload force. A preload of 600 grams may be necessary to accomplish the minimized tilt objective and compensate for preload fluctuations due to thermal cycling. This stability comes at the price of increased friction which leads to an increased size and power motor to overcome the friction and move the actuator arm. Increased friction also reduces the life of the bearing system.
An object of the present invention is to provide an actuator arm which requires less preloading force, but provides the same amount of physical stability over a large temperature range as the prior designs of actuator arm assemblies. Additionally, a reduced preload will increase the life of the bearing system.